Having now completed my Victoria copper penny series (with the exception of the Medusa and 1858 large rose, small date), this is how difficult I've found the difficult dates/varieties (a matter of availability rather than money):-
1839 proof - kept eluding me. Very difficult and the ones that did show up, very pricey. Had to eventually take the price plunge, otherwise I'd wait forever. Although if I'd waited, there's 2 at the upcoming Australian Noble auction.
1841 colon after REG: Scarce in mid grade. Very difficult in high grade.
1843 (all types) very difficult in high grade. No opportunity so far for anything above VF. Only sub fine for no colon after REG.
1845 - scarce at all levels. Finally got a decent one very recently (Interesting that although 1844 is technically, roughly the same as 1845 in terms of scarcity, there always seems to be 1844's on offer, but very few 1845's)
1847 Medusa: only saw the one on offer by Coopers Coins. Didn't buy for reasons now forgotten.
1849: A few available in the low to mid grades, but the high grade ones are excessively rare. I was extremely lucky with the one I got. Other than that I've seen an EF specimen, and the aUNC Waterbird example.
1853 PT: have to say, very rare, especially in high grade. I'm convinced Keith Bayford made a mistake offering a GEF example for just £125
1853 PT italic date: you just have to jump if you are lucky enough to see one. The fine example I bought from John (Stephen) Jerrams was sold as a PT specimen only. He didn't mention the italic date.
1854/3 - the real deal ones are extremely rare, and even more difficult in grades above fine.
1854 no colons - again very rare. Seen two, although probably a few unattributed ones have gone under the radar.
1856 OT - managed to obtain a fine example, and that's it. Dave Craddock did have an a/UNC with lustre specimen on offer for £1600 about a year back, but not surprisingly, by the time I called him, it had already gone. Excessively rare for availability at any grade.
1858 large rose large date: not seen one yet.
1860/59 - not as desperately rare as I'd feared, and did get an EF specimen with slight residual lustre.